A device including at least one antenna element and a dielectric lens is known, for example, from European Patent No. 498 524, in which a motor vehicle radar system for detecting vehicles traveling ahead is also described. This is a so-called bistatic radar sensor, i.e., a radar sensor with separate antennas for the send and receive paths. Independently of this peculiarity, each of the two antennas comprises a dielectric lens and at least one antenna element. In such a device, in particular in a transmitting antenna, the fact that the beam angle of the antenna element(s) is usually wider than the dielectric lens presents some difficulties. This means that part of the electromagnetic waves generated bypasses the dielectric lens. This portion is therefore not focused in the desired direction by the dielectric lens, which reduces the overall antenna yield.
In PCT International Publication No. WO 97/02496, a monostatic radar sensor is described, which is also provided for use in motor vehicles. Monostatic means that the same antenna is used for the transmission and receiving paths. In this case, it comprises at least three antenna elements and a dielectric lens arranged in front of these elements. In order to avoid overradiation of the lens when transmitting, a "polyrod" is arranged in front of each antenna element. This is understood as an approximately conical dielectric body, which, due to its dielectric properties, causes the electromagnetic waves generated to be prefocused. The exact adjustment of the individual polyrods presents difficulties, as even a very small deviation from the ideal position results in the lens being overradiated again.